text: # Copyright 2009-present MongoDB, Inc.
  #
  # Licensed under the Apache License, Version 2.0 (the "License");
  # you may not use this file except in compliance with the License.
  # You may obtain a copy of the License at
  #
  # http://www.apache.org/licenses/LICENSE-2.0
  #
  # Unless required by applicable law or agreed to in writing, software
  # distributed under the License is distributed on an "AS IS" BASIS,
  # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  # See the License for the specific language governing permissions and
  # limitations under the License.
  
  """Cursor class to iterate over Mongo query results."""
  
  import copy
  import datetime
  import warnings
  
  from collections import deque
  
  from bson import RE_TYPE
  from bson.code import Code
  from bson.py3compat import (iteritems,
                              integer_types,
                              string_type)
  from bson.son import SON
  from pymongo import helpers
  from pymongo.common import validate_boolean, validate_is_mapping
  from pymongo.collation import validate_collation_or_none
  from pymongo.errors import (AutoReconnect,
                              ConnectionFailure,
                              InvalidOperation,
                              NotMasterError,
                              OperationFailure)
  from pymongo.message import (_convert_exception,
                               _CursorAddress,
                               _GetMore,
                               _RawBatchGetMore,
                               _Query,
                               _RawBatchQuery)
  from pymongo.read_preferences import ReadPreference
  
  _QUERY_OPTIONS = {
      "tailable_cursor": 2,
      "slave_okay": 4,
      "oplog_replay": 8,
      "no_timeout": 16,
      "await_data": 32,
      "exhaust": 64,
      "partial": 128}
  
  
  class CursorType(object):
      NON_TAILABLE = 0
      """The standard cursor type."""
  
      TAILABLE = _QUERY_OPTIONS["tailable_cursor"]
      """The tailable cursor type.
  
      Tailable cursors are only for use with capped collections. They are not
      closed when the last data is retrieved but are kept open and the cursor
      location marks the final document position. If more data is received
      iteration of the cursor will continue from the last document received.
      """
  
      TAILABLE_AWAIT = TAILABLE | _QUERY_OPTIONS["await_data"]
      """A tailable cursor with the await option set.
  
      Creates a tailable cursor that will wait for a few seconds after returning
      the full result set so that it can capture and return additional data added
      during the query.
      """
  
      EXHAUST = _QUERY_OPTIONS["exhaust"]
      """An exhaust cursor.
  
      MongoDB will stream batched results to the client without waiting for the
      client to request each batch, reducing latency.
      """
  
  
  # This has to be an old style class due to
  # http://bugs.jython.org/issue1057
  class _SocketManager:
      """Used with exhaust cursors to ensure the socket is returned.
      """
      def __init__(self, sock, pool):
          self.sock = sock
          self.pool = pool
          self.__closed = False
  
      def __del__(self):
          self.close()
  
      def close(self):
          """Return this instance's socket to the connection pool.
          """
          if not self.__closed:
              self.__closed = True
              self.pool.return_socket(self.sock)
              self.sock, self.pool = None, None
  
  
  class Cursor(object):
      """A cursor / iterator over Mongo query results.
      """
      _query_class = _Query
      _getmore_class = _GetMore
  
      def __init__(self, collection, filter=None, projection=None, skip=0,
                   limit=0, no_cursor_timeout=False,
                   cursor_type=CursorType.NON_TAILABLE,
                   sort=None, allow_partial_results=False, oplog_replay=False,
                   modifiers=None, batch_size=0, manipulate=True,
                   collation=None, hint=None, max_scan=None, max_time_ms=None,
                   max=None, min=None, return_key=False, show_record_id=False,
                   snapshot=False, comment=None, session=None):
          """Create a new cursor.
  
          Should not be called directly by application developers - see
          :meth:`~pymongo.collection.Collection.find` instead.
  
          .. mongodoc:: cursors
          """
          # Initialize all attributes used in __del__ before possibly raising
          # an error to avoid attribute errors during garbage collection.
          self.__id = None
          self.__exhaust = False
          self.__exhaust_mgr = None
          self.__killed = False
  
          if session:
              self.__session = session
              self.__explicit_session = True
          else:
              self.__session = None
              self.__explicit_session = False
  
          spec = filter
          if spec is None:
              spec = {}
  
          validate_is_mapping("filter", spec)
          if not isinstance(skip, int):
              raise TypeError("skip must be an instance of int")
          if not isinstance(limit, int):
              raise TypeError("limit must be an instance of int")
          validate_boolean("no_cursor_timeout", no_cursor_timeout)
          if cursor_type not in (CursorType.NON_TAILABLE, CursorType.TAILABLE,
                                 CursorType.TAILABLE_AWAIT, CursorType.EXHAUST):
              raise ValueError("not a valid value for cursor_type")
          validate_boolean("allow_partial_results", allow_partial_results)
          validate_boolean("oplog_replay", oplog_replay)
          if modifiers is not None:
              warnings.warn("the 'modifiers' parameter is deprecated",
                            DeprecationWarning, stacklevel=2)
              validate_is_mapping("modifiers", modifiers)
          if not isinstance(batch_size, integer_types):
              raise TypeError("batch_size must be an integer")
          if batch_size < 0:
              raise ValueError("batch_size must be >= 0")
  
          if projection is not None:
              if not projection:
                  projection = {"_id": 1}
              projection = helpers._fields_list_to_dict(projection, "projection")
  
          self.__collection = collection
          self.__spec = spec
          self.__projection = projection
          self.__skip = skip
          self.__limit = limit
          self.__batch_size = batch_size
          self.__modifiers = modifiers and modifiers.copy() or {}
          self.__ordering = sort and helpers._index_document(sort) or None
          self.__max_scan = max_scan
          self.__explain = False
          self.__comment = comment
          self.__max_time_ms = max_time_ms
          self.__max_await_time_ms = None
          self.__max = max
          self.__min = min
          self.__manipulate = manipulate
          self.__collation = validate_collation_or_none(collation)
          self.__return_key = return_key
          self.__show_record_id = show_record_id
          self.__snapshot = snapshot
          self.__set_hint(hint)
  
          # Exhaust cursor support
          if cursor_type == CursorType.EXHAUST:
              if self.__collection.database.client.is_mongos:
                  raise InvalidOperation('Exhaust cursors are '
                                         'not supported by mongos')
              if limit:
                  raise InvalidOperation("Can't use limit and exhaust together.")
              self.__exhaust = True
  
          # This is ugly. People want to be able to do cursor[5:5] and
          # get an empty result set (old behavior was an
          # exception). It's hard to do that right, though, because the
          # server uses limit(0) to mean 'no limit'. So we set __empty
          # in that case and check for it when iterating. We also unset
          # it anytime we change __limit.
          self.__empty = False
  
          self.__data = deque()
          self.__address = None
          self.__retrieved = 0
  
          self.__codec_options = collection.codec_options
          # Read preference is set when the initial find is sent.
          self.__read_preference = None
          self.__read_concern = collection.read_concern
  
          self.__query_flags = cursor_type
          if no_cursor_timeout:
              self.__query_flags |= _QUERY_OPTIONS["no_timeout"]
          if allow_partial_results:
              self.__query_flags |= _QUERY_OPTIONS["partial"]
          if oplog_replay:
              self.__query_flags |= _QUERY_OPTIONS["oplog_replay"]
  
      @property
      def collection(self):
          """The :class:`~pymongo.collection.Collection` that this
          :class:`Cursor` is iterating.
          """
          return self.__collection
  
      @property
      def retrieved(self):
          """The number of documents retrieved so far.
          """
          return self.__retrieved
  
      def __del__(self):
          self.__die()
  
      def rewind(self):
          """Rewind this cursor to its unevaluated state.
  
          Reset this cursor if it has been partially or completely evaluated.
          Any options that are present on the cursor will remain in effect.
          Future iterating performed on this cursor will cause new queries to
          be sent to the server, even if the resultant data has already been
          retrieved by this cursor.
          """
          self.__data = deque()
          self.__id = None
          self.__address = None
          self.__retrieved = 0
          self.__killed = False
  
          return self
  
      def clone(self):
          """Get a clone of this cursor.
  
          Returns a new Cursor instance with options matching those that have
          been set on the current instance. The clone will be completely
          unevaluated, even if the current instance has been partially or
          completely evaluated.
          """
          return self._clone(True)
  
      def _clone(self, deepcopy=True, base=None):
          """Internal clone helper."""
          if not base:
              if self.__explicit_session:
                  base = self._clone_base(self.__session)
              else:
                  base = self._clone_base(None)
  
          values_to_clone = ("spec", "projection", "skip", "limit",
                             "max_time_ms", "max_await_time_ms", "comment",
                             "max", "min", "ordering", "explain", "hint",
                             "batch_size", "max_scan", "manipulate",
                             "query_flags", "modifiers", "collation")
          data = dict((k, v) for k, v in iteritems(self.__dict__)
                      if k.startswith('_Cursor__') and k[9:] in values_to_clone)
          if deepcopy:
              data = self._deepcopy(data)
          base.__dict__.update(data)
          return base
  
      def _clone_base(self, session):
          """Creates an empty Cursor object for information to be copied into.
          """
          return self.__class__(self.__collection, session=session)
  
      def __die(self, synchronous=False):
          """Closes this cursor.
          """
          already_killed = self.__killed
          self.__killed = True
          if self.__id and not already_killed:
              if self.__exhaust and self.__exhaust_mgr:
                  # If this is an exhaust cursor and we haven't completely
                  # exhausted the result set we *must* close the socket
                  # to stop the server from sending more data.
                  self.__exhaust_mgr.sock.close()
              else:
                  address = _CursorAddress(
                      self.__address, self.__collection.full_name)
                  if synchronous:
                      self.__collection.database.client._close_cursor_now(
                          self.__id, address, session=self.__session)
                  else:
                      # The cursor will be closed later in a different session.
                      self.__collection.database.client._close_cursor(
                          self.__id, address)
          if self.__exhaust and self.__exhaust_mgr:
              self.__exhaust_mgr.close()
          if self.__session and not self.__explicit_session:
              self.__session._end_session(lock=synchronous)
              self.__session = None
  
      def close(self):
          """Explicitly close / kill this cursor.
          """
          self.__die(True)
  
      def __query_spec(self):
          """Get the spec to use for a query.
          """
          operators = self.__modifiers.copy()
          if self.__ordering:
              operators["$orderby"] = self.__ordering
          if self.__explain:
              operators["$explain"] = True
          if self.__hint:
              operators["$hint"] = self.__hint
          if self.__comment:
              operators["$comment"] = self.__comment
          if self.__max_scan:
              operators["$maxScan"] = self.__max_scan
          if self.__max_time_ms is not None:
              operators["$maxTimeMS"] = self.__max_time_ms
          if self.__max:
              operators["$max"] = self.__max
          if self.__min:
              operators["$min"] = self.__min
          if self.__return_key:
              operators["$returnKey"] = self.__return_key
          if self.__show_record_id:
              # This is upgraded to showRecordId for MongoDB 3.2+ "find" command.
              operators["$showDiskLoc"] = self.__show_record_id
          if self.__snapshot:
              operators["$snapshot"] = self.__snapshot
  
          if operators:
              # Make a shallow copy so we can cleanly rewind or clone.
              spec = self.__spec.copy()
  
              # White-listed commands must be wrapped in $query.
              if "$query" not in spec:
                  # $query has to come first
                  spec = SON([("$query", spec)])
  
              if not isinstance(spec, SON):
                  # Ensure the spec is SON. As order is important this will
                  # ensure its set before merging in any extra operators.
                  spec = SON(spec)
  
              spec.update(operators)
              return spec
          # Have to wrap with $query if "query" is the first key.
          # We can't just use $query anytime "query" is a key as
          # that breaks commands like count and find_and_modify.
          # Checking spec.keys()[0] covers the case that the spec
          # was passed as an instance of SON or OrderedDict.
          elif ("query" in self.__spec and
                (len(self.__spec) == 1 or
                 next(iter(self.__spec)) == "query")):
              return SON({"$query": self.__spec})
  
          return self.__spec
  
      def __check_okay_to_chain(self):
          """Check if it is okay to chain more options onto this cursor.
          """
          if self.__retrieved or self.__id is not None:
              raise InvalidOperation("cannot set options after executing query")
  
      def add_option(self, mask):
          """Set arbitrary query flags using a bitmask.
  
          To set the tailable flag:
          cursor.add_option(2)
          """
          if not isinstance(mask, int):
              raise TypeError("mask must be an int")
          self.__check_okay_to_chain()
  
          if mask & _QUERY_OPTIONS["exhaust"]:
              if self.__limit:
                  raise InvalidOperation("Can't use limit and exhaust together.")
              if self.__collection.database.client.is_mongos:
                  raise InvalidOperation('Exhaust cursors are '
                                         'not supported by mongos')
              self.__exhaust = True
  
          self.__query_flags |= mask
          return self
  
      def remove_option(self, mask):
          """Unset arbitrary query flags using a bitmask.
  
          To unset the tailable flag:
          cursor.remove_option(2)
          """
          if not isinstance(mask, int):
              raise TypeError("mask must be an int")
          self.__check_okay_to_chain()
  
          if mask & _QUERY_OPTIONS["exhaust"]:
              self.__exhaust = False
  
          self.__query_flags &= ~mask
          return self
  
      def limit(self, limit):
          """Limits the number of results to be returned by this cursor.
  
          Raises :exc:`TypeError` if `limit` is not an integer. Raises
          :exc:`~pymongo.errors.InvalidOperation` if this :class:`Cursor`
          has already been used. The last `limit` applied to this cursor
          takes precedence. A limit of ``0`` is equivalent to no limit.
  
          :Parameters:
            - `limit`: the number of results to return
  
          .. mongodoc:: limit
          """
          if not isinstance(limit, integer_types):
              raise TypeError("limit must be an integer")
          if self.__exhaust:
              raise InvalidOperation("Can't use limit and exhaust together.")
          self.__check_okay_to_chain()
  
          self.__empty = False
          self.__limit = limit
          return self
  
      def batch_size(self, batch_size):
          """Limits the number of documents returned in one batch. Each batch
          requires a round trip to the server. It can be adjusted to optimize
          performance and limit data transfer.
  
          .. note:: batch_size can not override MongoDB's internal limits on the
             amount of data it will return to the client in a single batch (i.e
             if you set batch size to 1,000,000,000, MongoDB will currently only
             return 4-16MB of results per batch).
  
          Raises :exc:`TypeError` if `batch_size` is not an integer.
          Raises :exc:`ValueError` if `batch_size` is less than ``0``.
          Raises :exc:`~pymongo.errors.InvalidOperation` if this
          :class:`Cursor` has already been used. The last `batch_size`
          applied to this cursor takes precedence.
  
          :Parameters:
            - `batch_size`: The size of each batch of results requested.
          """
          if not isinstance(batch_size, integer_types):
              raise TypeError("batch_size must be an integer")
          if batch_size < 0:
              raise ValueError("batch_size must be >= 0")
          self.__check_okay_to_chain()
  
          self.__batch_size = batch_size
          return self
  
      def skip(self, skip):
          """Skips the first `skip` results of this cursor.
  
          Raises :exc:`TypeError` if `skip` is not an integer. Raises
          :exc:`ValueError` if `skip` is less than ``0``. Raises
          :exc:`~pymongo.errors.InvalidOperation` if this :class:`Cursor` has
          already been used. The last `skip` applied to this cursor takes
          precedence.
  
          :Parameters:
            - `skip`: the number of results to skip
          """
          if not isinstance(skip, integer_types):
              raise TypeError("skip must be an integer")
          if skip < 0:
              raise ValueError("skip must be >= 0")
          self.__check_okay_to_chain()
  
          self.__skip = skip
          return self
  
      def max_time_ms(self, max_time_ms):
          """Specifies a time limit for a query operation. If the specified
          time is exceeded, the operation will be aborted and
          :exc:`~pymongo.errors.ExecutionTimeout` is raised. If `max_time_ms`
          is ``None`` no limit is applied.
  
          Raises :exc:`TypeError` if `max_time_ms` is not an integer or ``None``.
          Raises :exc:`~pymongo.errors.InvalidOperation` if this :class:`Cursor`
          has already been used.
  
          :Parameters:
            - `max_time_ms`: the time limit after which the operation is aborted
          """
          if (not isinstance(max_time_ms, integer_types)
                  and max_time_ms is not None):
              raise TypeError("max_time_ms must be an integer or None")
          self.__check_okay_to_chain()
  
          self.__max_time_ms = max_time_ms
          return self
  
      def max_await_time_ms(self, max_await_time_ms):
          """Specifies a time limit for a getMore operation on a
          :attr:`~pymongo.cursor.CursorType.TAILABLE_AWAIT` cursor. For all other
          types of cursor max_await_time_ms is ignored.
  
          Raises :exc:`TypeError` if `max_await_time_ms` is not an integer or
          ``None``. Raises :exc:`~pymongo.errors.InvalidOperation` if this
          :class:`Cursor` has already been used.
  
          .. note:: `max_await_time_ms` requires server version **>= 3.2**
  
          :Parameters:
            - `max_await_time_ms`: the time limit after which the operation is
              aborted
  
          .. versionadded:: 3.2
          """
          if (not isinstance(max_await_time_ms, integer_types)
                  and max_await_time_ms is not None):
              raise TypeError("max_await_time_ms must be an integer or None")
          self.__check_okay_to_chain()
  
          # Ignore max_await_time_ms if not tailable or await_data is False.
          if self.__query_flags & CursorType.TAILABLE_AWAIT:
              self.__max_await_time_ms = max_await_time_ms
  
          return self
  
      def __getitem__(self, index):
          """Get a single document or a slice of documents from this cursor.
  
          Raises :class:`~pymongo.errors.InvalidOperation` if this
          cursor has already been used.
  
          To get a single document use an integral index, e.g.::
  
            >>> db.test.find()[50]
  
          An :class:`IndexError` will be raised if the index is negative
          or greater than the amount of documents in this cursor. Any
          limit previously applied to this cursor will be ignored.
  
          To get a slice of documents use a slice index, e.g.::
  
            >>> db.test.find()[20:25]
  
          This will return this cursor with a limit of ``5`` and skip of
          ``20`` applied.  Using a slice index will override any prior
          limits or skips applied to this cursor (including those
          applied through previous calls to this method). Raises
          :class:`IndexError` when the slice has a step, a negative
          start value, or a stop value less than or equal to the start
          value.
  
          :Parameters:
            - `index`: An integer or slice index to be applied to this cursor
          """
          self.__check_okay_to_chain()
          self.__empty = False
          if isinstance(index, slice):
              if index.step is not None:
                  raise IndexError("Cursor instances do not support slice steps")
  
              skip = 0
              if index.start is not None:
                  if index.start < 0:
                      raise IndexError("Cursor instances do not support "
                                       "negative indices")
                  skip = index.start
  
              if index.stop is not None:
                  limit = index.stop - skip
                  if limit < 0:
                      raise IndexError("stop index must be greater than start "
                                       "index for slice %r" % index)
                  if limit == 0:
                      self.__empty = True
              else:
                  limit = 0
  
              self.__skip = skip
              self.__limit = limit
              return self
  
          if isinstance(index, integer_types):
              if index < 0:
                  raise IndexError("Cursor instances do not support negative "
                                   "indices")
              clone = self.clone()
              clone.skip(index + self.__skip)
              clone.limit(-1)  # use a hard limit
              clone.__query_flags &= ~CursorType.TAILABLE_AWAIT  # PYTHON-1371
              for doc in clone:
                  return doc
              raise IndexError("no such item for Cursor instance")
          raise TypeError("index %r cannot be applied to Cursor "
                          "instances" % index)
  
      def max_scan(self, max_scan):
          """**DEPRECATED** - Limit the number of documents to scan when
          performing the query.
  
          Raises :class:`~pymongo.errors.InvalidOperation` if this
          cursor has already been used. Only the last :meth:`max_scan`
          applied to this cursor has any effect.
  
          :Parameters:
            - `max_scan`: the maximum number of documents to scan
  
          .. versionchanged:: 3.7
            Deprecated :meth:`max_scan`. Support for this option is deprecated in
            MongoDB 4.0. Use :meth:`max_time_ms` instead to limit server side
            execution time.
          """
          self.__check_okay_to_chain()
          self.__max_scan = max_scan
          return self
  
      def max(self, spec):
          """Adds `max` operator that specifies upper bound for specific index.
  
          :Parameters:
            - `spec`: a list of field, limit pairs specifying the exclusive
              upper bound for all keys of a specific index in order.
  
          .. versionadded:: 2.7
          """
          if not isinstance(spec, (list, tuple)):
              raise TypeError("spec must be an instance of list or tuple")
  
          self.__check_okay_to_chain()
          self.__max = SON(spec)
          return self
  
      def min(self, spec):
          """Adds `min` operator that specifies lower bound for specific index.
  
          :Parameters:
            - `spec`: a list of field, limit pairs specifying the inclusive
              lower bound for all keys of a specific index in order.
  
          .. versionadded:: 2.7
          """
          if not isinstance(spec, (list, tuple)):
              raise TypeError("spec must be an instance of list or tuple")
  
          self.__check_okay_to_chain()
          self.__min = SON(spec)
          return self
  
      def sort(self, key_or_list, direction=None):
          """Sorts this cursor's results.
  
          Pass a field name and a direction, either
          :data:`~pymongo.ASCENDING` or :data:`~pymongo.DESCENDING`::
  
              for doc in collection.find().sort('field', pymongo.ASCENDING):
                  print(doc)
  
          To sort by multiple fields, pass a list of (key, direction) pairs::
  
              for doc in collection.find().sort([
                      ('field1', pymongo.ASCENDING),
                      ('field2', pymongo.DESCENDING)]):
                  print(doc)
  
          Beginning with MongoDB version 2.6, text search results can be
          sorted by relevance::
  
              cursor = db.test.find(
                  {'$text': {'$search': 'some words'}},
                  {'score': {'$meta': 'textScore'}})
  
              # Sort by 'score' field.
              cursor.sort([('score', {'$meta': 'textScore'})])
  
              for doc in cursor:
                  print(doc)
  
          Raises :class:`~pymongo.errors.InvalidOperation` if this cursor has
          already been used. Only the last :meth:`sort` applied to this
          cursor has any effect.
  
          :Parameters:
            - `key_or_list`: a single key or a list of (key, direction)
              pairs specifying the keys to sort on
            - `direction` (optional): only used if `key_or_list` is a single
              key, if not given :data:`~pymongo.ASCENDING` is assumed
          """
          self.__check_okay_to_chain()
          keys = helpers._index_list(key_or_list, direction)
          self.__ordering = helpers._index_document(keys)
          return self
  
      def count(self, with_limit_and_skip=False):
          """**DEPRECATED** - Get the size of the results set for this query.
  
          The :meth:`count` method is deprecated and **not** supported in a
          transaction. Please use
          :meth:`~pymongo.collection.Collection.count_documents` instead.
  
          Returns the number of documents in the results set for this query. Does
          not take :meth:`limit` and :meth:`skip` into account by default - set
          `with_limit_and_skip` to ``True`` if that is the desired behavior.
          Raises :class:`~pymongo.errors.OperationFailure` on a database error.
  
          When used with MongoDB >= 2.6, :meth:`~count` uses any :meth:`~hint`
          applied to the query. In the following example the hint is passed to
          the count command:
  
            collection.find({'field': 'value'}).hint('field_1').count()
  
          The :meth:`count` method obeys the
          :attr:`~pymongo.collection.Collection.read_preference` of the
          :class:`~pymongo.collection.Collection` instance on which
          :meth:`~pymongo.collection.Collection.find` was called.
  
          :Parameters:
            - `with_limit_and_skip` (optional): take any :meth:`limit` or
              :meth:`skip` that has been applied to this cursor into account when
              getting the count
  
          .. note:: The `with_limit_and_skip` parameter requires server
             version **>= 1.1.4-**
  
          .. versionchanged:: 3.7
             Deprecated.
  
          .. versionchanged:: 2.8
             The :meth:`~count` method now supports :meth:`~hint`.
          """
          warnings.warn("count is deprecated. Use Collection.count_documents "
                        "instead.", DeprecationWarning, stacklevel=2)
          validate_boolean("with_limit_and_skip", with_limit_and_skip)
          cmd = SON([("count", self.__collection.name),
                     ("query", self.__spec)])
          if self.__max_time_ms is not None:
              cmd["maxTimeMS"] = self.__max_time_ms
          if self.__comment:
              cmd["$comment"] = self.__comment
  
          if self.__hint is not None:
              cmd["hint"] = self.__hint
  
          if with_limit_and_skip:
              if self.__limit:
                  cmd["limit"] = self.__limit
              if self.__skip:
                  cmd["skip"] = self.__skip
  
          return self.__collection._count(
              cmd, self.__collation, session=self.__session)
  
      def distinct(self, key):
          """Get a list of distinct values for `key` among all documents
          in the result set of this query.
  
          Raises :class:`TypeError` if `key` is not an instance of
          :class:`basestring` (:class:`str` in python 3).
  
          The :meth:`distinct` method obeys the
          :attr:`~pymongo.collection.Collection.read_preference` of the
          :class:`~pymongo.collection.Collection` instance on which
          :meth:`~pymongo.collection.Collection.find` was called.
  
          :Parameters:
            - `key`: name of key for which we want to get the distinct values
  
          .. seealso:: :meth:`pymongo.collection.Collection.distinct`
          """
          options = {}
          if self.__spec:
              options["query"] = self.__spec
          if self.__max_time_ms is not None:
              options['maxTimeMS'] = self.__max_time_ms
          if self.__comment:
              options['$comment'] = self.__comment
          if self.__collation is not None:
              options['collation'] = self.__collation
  
          return self.__collection.distinct(
              key, session=self.__session, **options)
  
      def explain(self):
          """Returns an explain plan record for this cursor.
  
          .. mongodoc:: explain
          """
          c = self.clone()
          c.__explain = True
  
          # always use a hard limit for explains
          if c.__limit:
              c.__limit = -abs(c.__limit)
          return next(c)
  
      def __set_hint(self, index):
          if index is None:
              self.__hint = None
              return
  
          if isinstance(index, string_type):
              self.__hint = index
          else:
              self.__hint = helpers._index_document(index)
  
      def hint(self, index):
          """Adds a 'hint', telling Mongo the proper index to use for the query.
  
          Judicious use of hints can greatly improve query
          performance. When doing a query on multiple fields (at least
          one of which is indexed) pass the indexed field as a hint to
          the query. Raises :class:`~pymongo.errors.OperationFailure` if the
          provided hint requires an index that does not exist on this collection,
          and raises :class:`~pymongo.errors.InvalidOperation` if this cursor has
          already been used.
  
          `index` should be an index as passed to
          :meth:`~pymongo.collection.Collection.create_index`
          (e.g. ``[('field', ASCENDING)]``) or the name of the index.
          If `index` is ``None`` any existing hint for this query is
          cleared. The last hint applied to this cursor takes precedence
          over all others.
  
          :Parameters:
            - `index`: index to hint on (as an index specifier)
  
          .. versionchanged:: 2.8
             The :meth:`~hint` method accepts the name of the index.
          """
          self.__check_okay_to_chain()
          self.__set_hint(index)
          return self
  
      def comment(self, comment):
          """Adds a 'comment' to the cursor.
  
          http://docs.mongodb.org/manual/reference/operator/comment/
  
          :Parameters:
            - `comment`: A string or document
  
          .. versionadded:: 2.7
          """
          self.__check_okay_to_chain()
          self.__comment = comment
          return self
  
      def where(self, code):
          """Adds a $where clause to this query.
  
          The `code` argument must be an instance of :class:`basestring`
          (:class:`str` in python 3) or :class:`~bson.code.Code`
          containing a JavaScript expression. This expression will be
          evaluated for each document scanned. Only those documents
          for which the expression evaluates to *true* will be returned
          as results. The keyword *this* refers to the object currently
          being scanned.
  
          Raises :class:`TypeError` if `code` is not an instance of
          :class:`basestring` (:class:`str` in python 3). Raises
          :class:`~pymongo.errors.InvalidOperation` if this
          :class:`Cursor` has already been used. Only the last call to
          :meth:`where` applied to a :class:`Cursor` has any effect.
  
          :Parameters:
            - `code`: JavaScript expression to use as a filter
          """
          self.__check_okay_to_chain()
          if not isinstance(code, Code):
              code = Code(code)
  
          self.__spec["$where"] = code
          return self
  
      def collation(self, collation):
          """Adds a :class:`~pymongo.collation.Collation` to this query.
  
          This option is only supported on MongoDB 3.4 and above.
  
          Raises :exc:`TypeError` if `collation` is not an instance of
          :class:`~pymongo.collation.Collation` or a ``dict``. Raises
          :exc:`~pymongo.errors.InvalidOperation` if this :class:`Cursor` has
          already been used. Only the last collation applied to this cursor has
          any effect.
  
          :Parameters:
            - `collation`: An instance of :class:`~pymongo.collation.Collation`.
          """
          self.__check_okay_to_chain()
          self.__collation = validate_collation_or_none(collation)
          return self
  
      def __send_message(self, operation):
          """Send a query or getmore operation and handles the response.
  
          If operation is ``None`` this is an exhaust cursor, which reads
          the next result batch off the exhaust socket instead of
          sending getMore messages to the server.
  
          Can raise ConnectionFailure.
          """
          client = self.__collection.database.client
          listeners = client._event_listeners
          publish = listeners.enabled_for_commands
          from_command = False
          start = datetime.datetime.now()
  
          def duration(): return datetime.datetime.now() - start
  
          if operation:
              try:
                  response = client._send_message_with_response(
                      operation, exhaust=self.__exhaust, address=self.__address)
                  self.__address = response.address
                  if self.__exhaust:
                      # 'response' is an ExhaustResponse.
                      self.__exhaust_mgr = _SocketManager(response.socket_info,
                                                          response.pool)
  
                  cmd_name = operation.name
                  reply = response.data
                  rqst_id = response.request_id
                  from_command = response.from_command
              except AutoReconnect:
                  # Don't try to send kill cursors on another socket
                  # or to another server. It can cause a _pinValue
                  # assertion on some server releases if we get here
                  # due to a socket timeout.
                  self.__killed = True
                  self.__die()
                  raise
          else:
              # Exhaust cursor - no getMore message.
              rqst_id = 0
              cmd_name = 'getMore'
              if publish:
                  # Fake a getMore command.
                  cmd = SON([('getMore', self.__id),
                             ('collection', self.__collection.name)])
                  if self.__batch_size:
                      cmd['batchSize'] = self.__batch_size
                  if self.__max_time_ms:
                      cmd['maxTimeMS'] = self.__max_time_ms
                  listeners.publish_command_start(
                      cmd, self.__collection.database.name, 0, self.__address)
              try:
                  reply = self.__exhaust_mgr.sock.receive_message(None)
              except Exception as exc:
                  if publish:
                      listeners.publish_command_failure(
                          duration(), _convert_exception(exc), cmd_name, rqst_id,
                          self.__address)
                  if isinstance(exc, ConnectionFailure):
                      self.__die()
                  raise
  
          try:
              with client._reset_on_error(self.__address, self.__session):
                  docs = self._unpack_response(reply,
                                               self.__id,
                                               self.__collection.codec_options)
                  if from_command:
                      first = docs[0]
                      client._process_response(first, self.__session)
                      helpers._check_command_response(first)
          except OperationFailure as exc:
              self.__killed = True
  
              # Make sure exhaust socket is returned immediately, if necessary.
              self.__die()
  
              if publish:
                  listeners.publish_command_failure(
                      duration(), exc.details, cmd_name, rqst_id, self.__address)
  
              # If this is a tailable cursor the error is likely
              # due to capped collection roll over. Setting
              # self.__killed to True ensures Cursor.alive will be
              # False. No need to re-raise.
              if self.__query_flags & _QUERY_OPTIONS["tailable_cursor"]:
                  return
              raise
          except NotMasterError as exc:
              # Don't send kill cursors to another server after a "not master"
              # error. It's completely pointless.
              self.__killed = True
  
              # Make sure exhaust socket is returned immediately, if necessary.
              self.__die()
  
              if publish:
                  listeners.publish_command_failure(
                      duration(), exc.details, cmd_name, rqst_id, self.__address)
  
              raise
          except Exception as exc:
              if publish:
                  listeners.publish_command_failure(
                      duration(), _convert_exception(exc), cmd_name, rqst_id,
                      self.__address)
              raise
  
          if publish:
              # Must publish in find / getMore / explain command response format.
              if from_command:
                  res = docs[0]
              elif cmd_name == "explain":
                  res = docs[0] if docs else {}
              else:
                  res = {"cursor": {"id": reply.cursor_id,
                                    "ns": self.__collection.full_name},
                         "ok": 1}
                  if cmd_name == "find":
                      res["cursor"]["firstBatch"] = docs
                  else:
                      res["cursor"]["nextBatch"] = docs
              listeners.publish_command_success(
                  duration(), res, cmd_name, rqst_id, self.__address)
  
          if from_command:
              if cmd_name != "explain":
                  cursor = docs[0]['cursor']
                  self.__id = cursor['id']
                  if cmd_name == 'find':
                      documents = cursor['firstBatch']
                  else:
                      documents = cursor['nextBatch']
                  self.__data = deque(documents)
                  self.__retrieved += len(documents)
              else:
                  self.__id = 0
                  self.__data = deque(docs)
                  self.__retrieved += len(docs)
          else:
              self.__id = reply.cursor_id
              self.__data = deque(docs)
              self.__retrieved += reply.number_returned
  
          if self.__id == 0:
              self.__killed = True
              # Don't wait for garbage collection to call __del__, return the
              # socket and the session to the pool now.
              self.__die()
  
          if self.__limit and self.__id and self.__limit <= self.__retrieved:
              self.__die()
  
      def _unpack_response(self, response, cursor_id, codec_options):
          return response.unpack_response(cursor_id, codec_options)
  
      def _read_preference(self):
          if self.__read_preference is None:
              # Save the read preference for getMore commands.
              self.__read_preference = self.__collection._read_preference_for(
                  self.session)
          return self.__read_preference
  
      def _refresh(self):
          """Refreshes the cursor with more data from Mongo.
  
          Returns the length of self.__data after refresh. Will exit early if
          self.__data is already non-empty. Raises OperationFailure when the
          cursor cannot be refreshed due to an error on the query.
          """
          if len(self.__data) or self.__killed:
              return len(self.__data)
  
          if not self.__session:
              self.__session = self.__collection.database.client._ensure_session()
  
          if self.__id is None:  # Query
              q = self._query_class(self.__query_flags,
                                    self.__collection.database.name,
                                    self.__collection.name,
                                    self.__skip,
                                    self.__query_spec(),
                                    self.__projection,
                                    self.__codec_options,
                                    self._read_preference(),
                                    self.__limit,
                                    self.__batch_size,
                                    self.__read_concern,
                                    self.__collation,
                                    self.__session,
                                    self.__collection.database.client)
              self.__send_message(q)
          elif self.__id:  # Get More
              if self.__limit:
                  limit = self.__limit - self.__retrieved
                  if self.__batch_size:
                      limit = min(limit, self.__batch_size)
              else:
                  limit = self.__batch_size
  
              # Exhaust cursors don't send getMore messages.
              if self.__exhaust:
                  self.__send_message(None)
              else:
                  g = self._getmore_class(self.__collection.database.name,
                                          self.__collection.name,
                                          limit,
                                          self.__id,
                                          self.__codec_options,
                                          self._read_preference(),
                                          self.__session,
                                          self.__collection.database.client,
                                          self.__max_await_time_ms)
                  self.__send_message(g)
  
          return len(self.__data)
  
      @property
      def alive(self):
          """Does this cursor have the potential to return more data?
  
          This is mostly useful with `tailable cursors
          <http://www.mongodb.org/display/DOCS/Tailable+Cursors>`_
          since they will stop iterating even though they *may* return more
          results in the future.
  
          With regular cursors, simply use a for loop instead of :attr:`alive`::
  
              for doc in collection.find():
                  print(doc)
  
          .. note:: Even if :attr:`alive` is True, :meth:`next` can raise
            :exc:`StopIteration`. :attr:`alive` can also be True while iterating
            a cursor from a failed server. In this case :attr:`alive` will
            return False after :meth:`next` fails to retrieve the next batch
            of results from the server.
          """
          return bool(len(self.__data) or (not self.__killed))
  
      @property
      def cursor_id(self):
          """Returns the id of the cursor
  
          Useful if you need to manage cursor ids and want to handle killing
          cursors manually using
          :meth:`~pymongo.mongo_client.MongoClient.kill_cursors`
  
          .. versionadded:: 2.2
          """
          return self.__id
  
      @property
      def address(self):
          """The (host, port) of the server used, or None.
  
          .. versionchanged:: 3.0
             Renamed from "conn_id".
          """
          return self.__address
  
      @property
      def session(self):
          """The cursor's :class:`~pymongo.client_session.ClientSession`, or None.
  
          .. versionadded:: 3.6
          """
          if self.__explicit_session:
              return self.__session
  
      def __iter__(self):
          return self
  
      def next(self):
          """Advance the cursor."""
          if self.__empty:
              raise StopIteration
          if len(self.__data) or self._refresh():
              if self.__manipulate:
                  _db = self.__collection.database
                  return _db._fix_outgoing(self.__data.popleft(),
                                           self.__collection)
              else:
                  return self.__data.popleft()
          else:
              raise StopIteration
  
      __next__ = next
  
      def __enter__(self):
          return self
  
      def __exit__(self, exc_type, exc_val, exc_tb):
          self.close()
  
      def __copy__(self):
          """Support function for `copy.copy()`.
  
          .. versionadded:: 2.4
          """
          return self._clone(deepcopy=False)
  
      def __deepcopy__(self, memo):
          """Support function for `copy.deepcopy()`.
  
          .. versionadded:: 2.4
          """
          return self._clone(deepcopy=True)
  
      def _deepcopy(self, x, memo=None):
          """Deepcopy helper for the data dictionary or list.
  
          Regular expressions cannot be deep copied but as they are immutable we
          don't have to copy them when cloning.
          """
          if not hasattr(x, 'items'):
              y, is_list, iterator = [], True, enumerate(x)
          else:
              y, is_list, iterator = {}, False, iteritems(x)
  
          if memo is None:
              memo = {}
          val_id = id(x)
          if val_id in memo:
              return memo.get(val_id)
          memo[val_id] = y
  
          for key, value in iterator:
              if isinstance(value, (dict, list)) and not isinstance(value, SON):
                  value = self._deepcopy(value, memo)
              elif not isinstance(value, RE_TYPE):
                  value = copy.deepcopy(value, memo)
  
              if is_list:
                  y.append(value)
              else:
                  if not isinstance(key, RE_TYPE):
                      key = copy.deepcopy(key, memo)
                  y[key] = value
          return y
  
  
  class RawBatchCursor(Cursor):
      """A cursor / iterator over raw batches of BSON data from a query result."""
  
      _query_class = _RawBatchQuery
      _getmore_class = _RawBatchGetMore
  
      def __init__(self, *args, **kwargs):
          """Create a new cursor / iterator over raw batches of BSON data.
  
          Should not be called directly by application developers -
          see :meth:`~pymongo.collection.Collection.find_raw_batches`
          instead.
  
          .. mongodoc:: cursors
          """
          manipulate = kwargs.get('manipulate')
          kwargs['manipulate'] = False
          super(RawBatchCursor, self).__init__(*args, **kwargs)
  
          # Throw only after cursor's initialized, to prevent errors in __del__.
          if manipulate:
              raise InvalidOperation(
                  "Cannot use RawBatchCursor with manipulate=True")
  
      def _unpack_response(self, response, cursor_id, codec_options):
          return response.raw_response(cursor_id)
  
      def explain(self):
          """Returns an explain plan record for this cursor.
  
          .. mongodoc:: explain
          """
          clone = self._clone(deepcopy=True, base=Cursor(self.collection))
          return clone.explain()
  
      def __getitem__(self, index):
          raise InvalidOperation("Cannot call __getitem__ on RawBatchCursor")
  